1. Field of the Invention
The invention relates to a heating unit for a corrugated-board manufacturing plant comprising heating elements that have a continuous heating surface extending in the direction of passage of at least two webs to be glued to each other, a drivable continuous conveyor belt, between the lower strand of which and the heating surface the webs to be glued to each other are accommodated, and at least one pressing device for charging the lower strand in the direction towards the heating surface.
2. Background Art
Heating units of the generic type have very thick heating plates, the upper side of which forms the heating surface, heating conduits for heating steam to pass through being provided in the heating plates. For these heating plates to exhibit a plane heating surface as a support for the web of corrugated board to be produced, they must be extraordinarily thick, for instance 150 mm. These heating plates consisting of solid cast iron or a steel structure are characterized by high material requirements. This restfits in heat strongly accumulating in the heating plate so that it reacts rather lazily to changes in heat demand in the case of fluctuations of speed and quality change-over. Since the heat demand cannot be adjusted, defaults will occur such as corrugated board that is crooked or not correctly glued, reductions of speed and quality losses, i.e. there will be restrictions of production, and scrap.
A heating plate for a heating unit of the generic type is known from DE-AS 2 213 745, in which any distorsion of the heating plate by temperature differences is encountered in that support members to which to apply tensile load are provided at the four comers of the heating plate, the remaining edges of the heating plate being provided with support members to which to apply pressure. The support members disposed at the comers are to prevent the heating plate from bending upwardly, while the other support members to which to apply pressure are to oppose any sagging of the heating plate.
DE 42 15 086 A1 teaches, in a heating unit for a corrugated-board manufacturing plant, to secure the heating plates by means of a fastening such that they are adjustable to form a horizontal heating surface. To this end, the heating plates are fixed in a rigid and stationary frame. Further, the ends of the heating plates are supported by way of movable beatings.